Highly pressurized, ultra high pure fluids, particularly carbon dioxide, are required for a variety of industrial processes. For example, some of the evolving applications in the electronic industry demand the use of supercritical carbon dioxide at high flow rates and high pressures. One of the methods for achieving high pressure carbon dioxide has been to pump liquid carbon dioxide to a required pressure. However, pumping liquid carbon dioxide to a high pressure can introduce impurities, such as particulates, hydrocarbons, halocarbons, etc., to the product stream.
Other applications, such as photo-resist removal, deposition, lithography, etc, may require an ultra high purity (UHP) process liquid such as carbon dioxide delivered to a point of use (POU) processing chamber at elevated pressures that range from 2,000 psig to 10,000 psig. The latter applications depend upon many factors such as, for example, specifics of an application, tool design, process philosophy, etc.
Processes for delivery of high pressure gases including carbon dioxide are known. Some of these processes may attempt to deliver UHP, high pressure vapor using, for example, a pump free system to elevate the vapor pressure while preserving gas purity. U.S. Pat. No. 6,023,933 discloses a process, which is capable of delivering UHP argon vapor at pressures up to 67,000 psig. In the '933 patent, a high purity gas is provided in a liquefied physical state, introduced to a vaporization vessel, and then heated in an isochoric vaporizer sufficiently to vaporize the liquefied gas. As the liquid is vaporized in the isochoric vaporizer, the pressure builds to pressures ranging from 10,000 to 67,000 psig. When the liquid is substantially vaporized, another unit is used for vapor delivery.
U.S. Pat. No. 6,327,872 discloses a process for delivering liquid carbon dioxide to a point of use at pressures of 750 to 1071 psig. The '872 patent acknowledges in the background the production of high-pressure liquid delivery systems up to about 68 bar by means of a pump and the problems associated therewith. The '872 patent teaches delivering liquid carbon dioxide to an accumulation vessel and then heating the liquid carbon dioxide contained therein thereby elevating the pressure. Using this method is possible to elevate liquid carbon dioxide from a bulk supply pressure of approximately 300 psig to a maximum of about 1071 psig. If isochoric heating continues above the critical point of about 31° C. and pressure of about 1071 psig, liquid carbon dioxide may be converted into a supercritical fluid. Further, the use of different fluid (other then purified carbon dioxide) can potentially lead to delivered product contamination.
There are also known processes and apparatuses for producing a multiphase slush. The majority of these processes and apparatuses, however, may not be suitable for UHP applications because they incorporate parts such as stirrers, augers, scrapers, pumps, etc. that are potential sources of product contamination. For example, U.S. Pat. Nos. 5,402,649 and 5,168,710 and European application EP0523568 each teach a H2 slush producing method and apparatus that operates under vacuum conditions and incorporates one or more stirring devices. JP 09113128 teaches a method for generating and apparatus for producing H2 slush using a surface scraper to separate solidified gas from a surface. JP 06281321 A describes a device that creates solid H2 on a liquid surface using a coolant. The coolant has a temperature below the H2 freezing point and a mixing device is used to create slush H2.
Still other references describe slush creation by injecting of “freezing centers” into a liquid phase. For example, WO 0033665 describes producing a CO2 slush by first injecting a CO2 gas into an aqueous type solution. The solution solidifies due to temperature drop as a predetermined pressure is achieved. U.S. Pat. No. 6,405,541 and published U.S. patent application 20010041210 A1 describe solid particle injection into a liquefied gas to create slush.
EP 1033543 A2 describes a slush generation and collection process. The downside of the invention is that it uses an external cooling source to freeze liquid on a cooled surface, and that it is focused on cryogenic liquids such as oxygen, nitrogen, helium, and water.
U.S. Pat. No. 3,667,242 presents an apparatus for a CO2 snow making process, but does not offer a slush creation process and a collector for holding slush.